Data communications networks often include elements that are connected by a wireless link. There are many benefits to a wireless connection, in particular providing the mobility of a wirelessly connected device and the convenience and potential cost savings associated with the reduction of wired infrastructure. Typically, a number of static wireless access points may be deployed within a local zone to which mobile devices may form wireless connections, the connections typically conforming to an industry standard such as an IEEE 802.11 standard, for example IEEE 802.11n. Preferably the wireless connection points are arranged in such a way as to give useful coverage in the zone concerned and are connected to a data network by wired or wireless links. However, the wireless bandwidth available is typically subject to limitations due to spectrum allocation imposed by regulatory authorities and so it is desirable to ensure that the wireless resource is used in an efficient manner. This is typically achieved by careful planning of the siting, transmission power and frequency of operation of the wireless connection points.
With the growth of the use of wireless networks, it is becoming increasingly likely that a wireless network may lie adjacent to another network. For example, a network may be next to a network used by a different enterprise occupying an adjacent building, so that it is possible that interference will be experienced between the networks. Furthermore, it is often undesirable that a wireless connection is possible outside a desired zone of coverage due to considerations of network security. It is accordingly desirable to restrict coverage to within a defined zone, typically a building or enterprise. A location may be said to have wireless coverage if a signal may be received at that location with an acceptable quality; there are a number of well known measures of signal quality that may be used to define coverage, among them signal power level, signal-to-noise-and-interference ratio and bit error rate. Typically, a wireless network may operate in an unlicensed band, for example the industrial, scientific and medical unlicensed bands at approximately 2.4 GHz or 5 GHz, in which many other devices such as video senders may operate. What is more, devices such as microwave ovens may emit spurious signals within these bands, potentially interfering with operation of a wireless network operating within the same frequency band.
It is known to use sensors as an aid to planning a wireless network in terms of the siting, transmission power and operating frequency of access points; such sensors may measure the received signal power of transmissions from access points within the network, as well as detecting interfering signals from other networks and other devices. The received signal power is related to radio frequency field strength at the location of the antenna of the sensor, according to the gain of the antenna. A measure of received signal power can thus be used as an indication of the radio frequency field strength. Such sensors are typically hand held devices, and may be used, for example, to search for active access points in a given zone. Sensors may perform a spectrum analysis function to identify frequencies that are occupied by signals and interference, and signal analysis to distinguish signals from interference. Sensors can perform a search for available access points, the search involving passive or active scanning; passive scanning simply involves measurement of received signals and active scanning involves sending a beacon probe, to which available access points may be programmed to respond.
It is known that sensors may be connected to a server and a network management station, as for example as disclosed in U.S. Pat. No. 7,184,777. Such a system may include a performance manager to initiate actions to mitigate the impact of current radio frequency conditions. The performance manager may configure access points to operate on other channels or adjust the transmit power of an access point in response to a high level of interference detected by sensors.
Typically, wireless network planning may be carried out with the aid of a planning tool, such as the Nortel WLAN Management Software 2300 Series. Such tools typically provide a method of entering a map of a zone in which wireless coverage is required into a model, and an operator may add details of known radio frequency obstructions to the map. The tool may predict radio frequency coverage within the zone, and the operating powers and frequencies may be adjustable within the model to give a required coverage zone. However, the accuracy of the model is limited by the data input by an operator; propagation conditions may be complex and not all radio frequency obstructions and reflections may be recognised. Furthermore, the flexibility in siting access points may be limited by practical constraints, and adjustment of the transmit power and operating frequency of access points gives a limited scope for optimizing coverage.
It is an object of the present invention to provide a method and apparatus which addresses these disadvantages.